In a heartfelt open letter to the city of Boston for The Players’ Tribune, Isaiah Thomas expressed excitement over the prospect of playing with LeBron James on the Cleveland Cavaliers, but what came through most clearly was how deeply the All-Star point guard was hurt by the trade from the Celtics.

Thomas began his story with an account of an awkward phone call with president of basketball operations Danny Ainge, who transitioned from a conversation about his All-NBA player’s one-year wedding anniversary vacation to this: “I just traded you.” As Ainge went on to say how much Thomas had done for the organization, the ex-Celtic said he just wanted to end the call and ultimately did.

“It was basically, you know — I appreciate you reaching out, appreciate you telling me, but there’s really nothing else that you or I need to be saying right now,” Thomas wrote on the eve of a Cavaliers news conference introducing him and Boston teammates Jae Crowder and Ante Zizic to Cleveland.

Thomas used the ensuing phone calls to his two young sons, James and Jaiden, to detail the painful dichotomy of joining LeBron and leaving the Celtics. James said, “LEBRON! LEBRON JAMES! Dad — Dad. You get to play with LeBron James!” But Jaiden felt sadness about saying goodbye to Boston, a place the Thomas family had made home, where the boys were scheduled to start school this month.

From there, Thomas poured his heart out about a relationship with the city that has left him heartbroken. It was a reminder of the reality behind professional sports trades, one Thomas hopes will help fans better understand decisions like Kevin Durant’s to leave loyalty out of this business.

Passages like this stood out for their candor:

But yeah, I’ll just say it: That s*** hurt. It hurt a lot.

And I won’t lie — it still hurts.

It’s not that I don’t understand it. Of course I get it: This is a business. Danny is a businessman, and he made a business move. I don’t agree with it, just personally, and I don’t think the Boston Celtics got better by making this trade. But that’s not my job. That’s Danny’s. And it’s a tough job, and he’s been really good at it. But at the end of the day, these deals just come down to one thing: business. So it’s no hard feelings on that end. I’m a grown man, and I know what I got into when I joined this league — and so far it’s been more blessings than curses. I’m not sitting here, writing this, because I feel I was wronged. I wasn’t wronged. It was Boston’s right to trade me.

And for every call back to reality, Thomas tugged at the heartstrings again:

At the same time, though, people gotta understand. Like, even with all of this being said … man … it still hurt. It still hurt bad. And I hope people can understand that when I say it hurt, it isn’t directed at anyone. I’m not saying I was hurt by anyone, or wronged by anyone, or betrayed. I’m just saying, man, I’m only human. I may act like a tough guy on the court. And I may seem like I have ice in my veins when I’m competing. But at the same time — it ain’t ice, really. I got blood and I got a heart like everyone else.

And so when I say this hurts, man — just know that it isn’t because of anything anyone else did. It’s only because of something I did.

I fell in love with Boston.

Thomas did not address concerns over his hip injury that led the Cavaliers to hold up the trade and has resulted in reports speculating that he could miss significant time this season before becoming an unrestricted free agent next summer. He did, however, write, “I get to come over and join the best team in the East, and try to win a championship alongside the best basketball player in the world.”

But for every mention of the Cavs, there were a handful more stories about how sad he is to leave Boston behind. “Man, am I going to miss being a Celtic,” wrote Thomas, describing how the organization helped him evolve from merely instant offense off the bench to a top-five MVP candidate. “The Boston Celtics let me have a chance to be great,” he added. “And I’ll never forget that.”

Thomas expressed a kinship with Celtics fans over a shared desire to speed up what was a rebuilding process. Or, as he put it: “Man, f*** the lottery.” He thanked them for their compassion in the aftermath of his sister’s death. “Honestly,” he said, “it felt like the whole city of Boston was with me.”

He wished he could have been to the Celtics what Tom Brady is to the New England Patriots or David Ortiz was to the Red Sox. And he revealed the one thing that would make him truly happy about his time in Boston: a parent telling a child he became a Celtics fan because, “I saw Isaiah Thomas play.”

But for anyone in Cleveland who might be feeling a little left out right now, Thomas left you with this:

Of course, being on the team the East runs through now … I won’t lie, it’s some mixed emotions. Because that was our goal in Boston for so long — get through the Cavs, and win the East. And I know that’s still Boston’s goal. But now, it’s like, I’m the one who has to stop them from reaching it. And that’s tough. Because come playoff time, if and when we have to face the Celtics … I don’t know, it’s hard to explain. But that won’t just be “the team I used to be on.” That’s my old team. The elite offense, the 30-some national TV games, the becoming a place where free agents want to come and play — I feel like I helped build that. I helped create that.

And come playoffs, all of a sudden, it’ll be like, O.K., now destroy it.

It’s sad, man. It’s just sad.

But I didn’t come to Cleveland to lose.

The Cavaliers open their 2017-18 schedule against the Celtics in Cleveland on national television on Oct. 17. Whether Thomas will be in uniform or not, it will be an emotional night for the 5-foot-9 star, and undoubtedly fans from both cities will be pulling for him. He tends to have that effect on people.